text: Britain was initially involved in the development of the metric system, and the US was among the 17 initial signatories of the Metre Convention in 1875. Yet in spite of enthusiastic support for the new system by intellectuals such as Charles Dickens, these two countries were particularly slow to implement it.
  In the US, the metric system replaced the apothecaries' system in the United States Pharmacopeia of 1971.
  In the UK, metric drug measurements were required for dealings in drugs from January 1, 1971.